Here is the full list of all 31 Sheep's Symphony achievements.
Complete a song on the "D&B" stage
Complete the tutorial
Achieve an S rank on "Tutorial"
Achieve an S rank on "Wild Josie"
Achieve an S rank on "Wanderlust"
Achieve an S rank on "Trapgrind"
Achieve an S rank on "Final"
Achieve an S rank on "Racecar"
Achieve an S rank on "Industry"
Achieve an S rank on "Serien"
Achieve an S rank on "Hate Mail"
Achieve an S rank on "2ez"
Achieve an S rank on "Vampire"
Achieve an S rank on "Exotic Animal Kissing Booth"
Achieve an S rank on 7 different songs
Complete a song while wearing 30 different outfits
Reach the #1 spot on any song's leaderboard
Click the channel link in the menu
Achieve a B rank or higher in 4 Shiester songs
Complete a song with the "Elf" enemy selected
Complete a song with the "Gray" enemy selected on a Wednesday
Retry a song from the pause menu 10 times in a row
Achieve a 100 combo
Achieve a 300 combo
Achieve a 500 combo
Achieve an S rank on "angelz den"
Achieve an S rank on "DREAMS"
Achieve an S rank on "FOREVER"
Achieve an S rank on "goredance"
Achieve an S rank on "Skinwalker"
Achieve an S rank on "Geocode"